Composite concrete columns of 3DP concrete and self-compacting concrete subjected to normal force

Conventional concrete columns are cast in forms made of steel or wood. The work of erecting and dismantling the formwork is time-consuming and laborious. Steel forms can be used several times but wood forms are usually only used once or a small number of times but in both cases additional materials are necessary for completing the columns. By using 3D Printed Concrete (3DPC) as lost forms, the work can be more efficient. If composite action between the form and the concrete core can be reached, also material savings with connected reductions in CO2 emissions can be achieved by combining a high performance concrete form with a concrete core of moderate strength. The process can be even more efficient by using Self Compacting Concrete (SCC) in the core. One BSc and one MSc thesis project on small specimens of this type has beenconducted with promising result at KTH. That led to the successful application
of a larger experimental program containing both load tests and tests on durability. This paper focuses on four composite and two homogeneous SCC beams that were produced and subjected to normal force up to failure. The specimens were 3 m long and had a circular cross section with a diameter = 0,3 m. The composite columns reached failure loads that corresponded well to the ones of the homogeneous columns. After the loading tests, the bond between the form and the core was tested using pull-off tests of cores drilled from the columns in areas without failure zones. The average bond strength value was 1,75 MPa which is in the same range as frequent values in laboratory tests of bond between concrete and concrete and an additional indication of composite actions.